G protein-coupled receptors (GPCRs) are one of the most important families of pharmaceutical targets. However, some of the most desirable types of GPCR drugs have also been some of the most difficult to discover. GPCRs are integral membrane proteins that are traditionally studied in live cells or cell membrane preparations, sources that limit the ability to purify and manipulate GPCR proteins. These limitations have hindered the discovery of drugs against many important GPCRs and drugs with pharmacologically-specific mechanisms of action. A novel method that aids in discovering new and improved GPCR drugs could have a major impact on human health. We have demonstrated the feasibility of a unique assay system for GPCR activation that offers the benefits of a cell-based system (relevant signaling pathways) without their drawbacks. Our strategy involves the use of a novel technology, the Lipoparticle that enables structurally-intact GPCRs to be purified away from cells and assayed for activity. The Specific Aims of our proposal are: I. Test the LipoSignal assay for screening diverse GPCR activators and inhibitors II. Develop the LipoSignal assay to target pharmacologically distinguishable GPCR signaling mechanisms III. Format a LipoSignal Array to identify GPCR cross-reactivity and orphan GPCR-ligand pairs. PUBLIC HEALTH RELEVANCE: The product that results from this proposal will contribute to public health and the cure of human diseases by providing a novel approach for identifying better drugs and new ligands against GPCRs. The chemokines receptors, including CXCR4 and CCR5, are involved in cancer, inflammatory diseases, and HIV infection, and are a major focus of this proposal. However, our technology has broad application to a diverse range of GPCRs, and also has the capability of being used to identify cell- and signaling pathway-specific GPCR drugs that are difficult to identify using conventional assays. As a result of this proposal, we expect to commercialize a product that will lead directly to the development of new and improved GPCR drugs.